1. Field of the Invention
This invention relates to improvements in an airbag, and more particularly to the improvements in a side airbag which is light in weight, compact-storable and high in gas-tight sealing characteristics.
2. Description of the Prior Art
Recently, airbag systems have been extensively used for safely protecting vehicle occupants. In the airbag systems, the number of airbags used within a passenger compartment has been increasing, including an airbag for a driver, an airbag for a vehicle passenger on a front seat, a side airbag for protection in side collision and an airbag for a passenger on a rear seat. Of these airbags, attention has been paid particularly on the side airbag for protecting the vehicle occupant from impact in a side collision, in order to further increase safety for the vehicle occupants.
The side airbag is inflated and developed in a narrow space between a vehicular seat and a vehicle body and therefore is required to be small in size and volume while sufficiently protecting the vehicle occupant. Additionally, the side airbag is required not to cause such problems as to unnecessarily inflate during its development thereby not to sufficiently absorb impact energy of the vehicle occupant, or as to strike against the vehicle occupant and provide the vehicle occupant with impact. Particularly, a kind of the side airbag, i.e., an inflatable curtain is required to maintain a high gas-tight sealing ability so that gas cannot leak from the airbag throughout a long time after development of the airbag in order to protect the head of the vehicle occupant even if the vehicle rolls under impact of a side collision. The inflatable curtain is arranged to develop along a side window so as to cover whole or a part of the window in order to protect the vehicle occupant from being injured upon severe striking against the side window or a section around it under impact of the side collision. Furthermore, the inflatable curtain is required to be small in volume and cross-sectional area in its folded state since a space for storing the inflatable curtain is very narrow, for example, around pillars or roof side rails.
A variety of propositions for obtaining airbags to be used as the above side airbag have been made. Japanese Patent Provisional Publication No. 10-109607 discloses an side airbag which is woven as a tubular structure by hollow weave, in which two woven cloths are joined through a joining portion. The whole tubular structure is coated with coating material impervious to gas, thereby obtaining the side airbag of no sewing. This side airbag has a hollow section which is outlined by curved lines. The tubular structure of this side airbag is usually woven by a loom equipped with a jacquard machine as proposed, for example, in Japanese Patent Provisional Publication No. 1-254446. As well known, with the jacquard machine, opening in shedding operation is accomplished by vertically moving a thread for hanging each warp yarn of a cloth, so that a high density cloth for the airbag or the like requires large a large total number of warp yarns. Accordingly, the number of jacquard machines increases as the denier of warp yarns decreases thus raising production cost, while maintenance is required for many hanging threads thus complicating production process.
A proposition for reducing the space in which an airbag is stored has been made by forming the airbag of very thin cloth formed of yarns of lower denier and by folding the airbag compact, as disclosed in U.S. Pat. No. 5,482,317. In this proposition, the airbag is woven using nylon 66 yarns having 45 to 140 denier. The weight of the woven cloth per unit area is considerably low as compared with other conventional cloths for airbags. Here, the mechanical characteristics of the cloth itself is low as compared with other conventional cloths, and therefore the airbag of this proposition is formed to have a rectangular outer peripheral shape so as to make unnecessary sewing at an outer peripheral section thus to ensure a pressure resistance of the airbag. However, it is difficult that the airbag of this proposition is applied to airbags having complicated shapes, such as side airbags.